In high speed data processing systems, magnetic recording has been employed for large memory capacity requirements. Data is read from and written onto the magnetic recordings using magnetic transducers commonly called magnetic heads which are positioned adjacent to the magnetic recording medium. For a contact recording, wherein the magnetic recording medium comes in contact with the magnetic head, the pole pieces are generally made of a magnetic ferrite material because of its wearing characteristics. The magnetic ferrite pole pieces, while having good wearing characteristics for the contact recording particularly with magnetic tape, however, lack the efficiency to record on high coercivity recording medium in the higher data density requirements for present day data recording. Magnetic heads having thin film pole pieces were developed to increase the saturation moment of the pole pieces and to increase the operating efficiency of the transducers, especially in the write or data recording procedure.
Thin film pole pieces, however, while providing the required efficiency to write the higher data density requirements, could not withstand the abrasion of the magnetic recording medium, especially in the contact recording situation. A first order requirement for high density recording is the minimizing of spacing between the surface of the media and the functional recording gap between the pole pieces. With the soft magnetic material thin film poletips of nickel-iron, for instance, the functional recording gap and the poletips are susceptible to wear by the media. Increasing the spacing between the recording gap and the media deteriorates the recording performance.
The write saturation performance characteristics of an interleaved, bi-directional, magnetic head operating in ferrite-trailing mode are not as good as those during operation in poletip-trailing mode. The mode of operation depends on the direction of tape travel: during ferrite-trailing mode, the tape travels across the gap towards the deposited poletip; in poletip-trailing mode, the tape travels towards the ferrite poletip. Regardless of write mode, a head experiences amplitude loss at high write currents. However, because of the lower saturation moment of the ferrite poletip compared to that of the deposited poletip, the amplitude loss is significantly more severe in ferrite-trailing mode. The problem thus presented is how to better balance the saturation moments of the poletips.
FIG 1A shows a typical conventional thin film magnetic head for use in contact recording on flexible magnetic media, such as magnetic tape. The prior art thin film magnetic head of FIG 1A includes a non-magnetic substrate 1, generally made of a non-magnetic ceramic. A first thin film pole piece 2, generally made of a Permalloy; i.e., a nickel-iron material, is deposited onto the substrate 1. A second thin film pole piece 3 of the same nickel-iron material is deposited onto an insulating layer 4 which encompasses the coil conductors 5 and forms a magnetic gap 6. A support and leveling material 7, generally non-magnetic, is deposited onto the second pole piece 3. The support material 7 is then covered by a non-magnetic closure piece 8. A magnetic tape media moves in a direction as shown by arrow 9 operating in a motion transverse to the pole pieces 2 and 3 over an air-bearing surface (ABS) where the contact recording takes place.
FIG 1B depicts a likely gap erosion profile on the ABS of a standard thin film recording head after wear as a result of the magnetic tape coming in contact at the ABS. Referring to FIG 1B, the thin film pole pieces 2 and 3 are soft compared to the ceramic substrate 1 and the ceramic closure 8. The greatest erosion caused by the contact recording is in the functional gap region 6 and is identified as gap erosion. The erosion is generally also great in the support material 7, but generally this area is far enough away from the functional gap region 6 as not to be a primary concern. The effective gap spacing from the ABS can easily be several microinches. At a recording density of 2300 flux changes per micrometer the signal loss for each microinch of spacing is 1.58 decibels. It is, therefore, essential to minimize effective gap erosion to achieve high density recording objectives.
Based on write saturation characteristics, it is best to use a thin film pole piece as the trailing pole piece for the write mode of magnetic heads. The write saturation characteristics in the use of a trailing pole piece of a block of magnetic ferrite material are not as good at short wavelengths, see FIG 1C. In FIG 1D, a curve shows the output amplitude of magnetic transitions when the write current is increased in a thin film trailing pole piece, such as the head of FIG 1A. In FIG 1D, the output amplitude is higher at its peak with approximately 60 milliamperes of write current and has a good output when 100 milliamperes of write current is applied to the head. The ferrite block amplitude output of FIG 1C is lower at its peak and is essentially zero at a high write current of 100 milliamperes. The degradation of the amplitude output is attributed to the lower saturation moment of the ferrite material as compared to the nickel-iron material normally used for thin film pole pieces. What is needed is a magnetic head that has the wear characteristics of a ferrite block trailing pole piece and the amplitude output of a thin film trailing pole piece.
Prior attempts to lessen the gap erosion include the use of a magnetic ferrite substrate as the first pole piece and a thin film magnetic layer as the second pole piece. This would have the affect of lowering the gap erosion, but balancing the saturation moment of the completely different pole piece materials caused insurmountable problems, especially with the flexible magnetic media that must be operational in both directions and, therefore, must operate in a trailing magnetic ferrite mode.
The present invention, therefore, provides for an improved magnetic head for contact recording that lowers the erosion as a result of the contact at the functional magnetic gap region, while providing pole pieces that have a balanced saturation moment.